In a trunked radio data communications system using half-duplex radios, plural data messages are exchanged over a single RF working channel using a technique where a working channel repeater assigned to a data call sends status messages to both the data originating radio and the data receiving radio...http://www.google.com.tw/patents/US5734643?utm_source=gb-gplus-share專利 US5734643 - Method and apparatus for transmitting data over a radio communications network 
